In a conventional pneumatic tyre of the “tubeless” type (that is to say of the type without an inner tube), the radially internal face comprises an airtight layer (or more generally a layer airtight to any inflation gas) which makes it possible to inflate the pneumatic tyre and to keep it under pressure. Its airtightness properties allow it to guarantee a relatively low level of pressure loss, making it possible to keep the tyre inflated in a normal operating state for a sufficient period of time, normally of several weeks or several months. Another role of this layer is to protect the carcass reinforcement and more generally the remainder of the tyre from the risk of oxidation due to the diffusion of air originating from the space interior to the tyre.
This role of airtight inner layer or “inner liner” is today fulfilled by compositions based on butyl rubber (copolymer of isobutylene and isoprene), which have been recognized for a very long time for their excellent airtightness properties.
However, a well-known disadvantage of compositions based on butyl rubber is that they exhibit high hysteresis losses, furthermore over a broad temperature spectrum, which disadvantage is damaging to the rolling resistance of the pneumatic tyres.
To reduce the hysteresis of these airtight inner layers and thus, in the end, the fuel consumption of motor vehicles is a general objective which current technology comes up against.
Document WO 2009/007064 of the Applicant companies discloses a pneumatic object provided with a layer airtight to the inflation gases, in which the airtight layer comprises an elastomer composition comprising at least a styrene thermoplastic (TPS) elastomer, a platy filler and optionally a polybutene oil. In comparison with a butyl rubber, the TPS elastomer exhibits the major advantage, due to its thermoplastic nature, of being able to be worked as is in the molten (liquid) state and consequently of offering the possibility of simplified processing while ensuring an airtightness at least equal to if not greater than that obtained with a conventional airtight layer made of butyl rubber.
A limitation of the endurance performance of these airtight layers is however observed when the content of platy fillers becomes significant.